RU2866309C2 - Method for producing inorganic filtration media by interleaving and resulting membrane - Google Patents

Abstract

FIELD: 3D printing.

SUBSTANCE: invention relates to a method for producing a monolithic inorganic porous carrier using a 3D printing machine comprising at least one extrusion head adapted for movement in space. The extrusion head is controlled along a digital path so that, for an overlapping path, the material, during application, partially overlaps at least one edge of a previously applied layer of material with an overlapping portion of the material present in its thickness and having a thickness strictly less than the nominal height, in order to avoid spaces between the rounded edges of the applied layer of material and the edges of the previously applied layer of material; for a crossing path, the material, during application, crosses at least one previously applied layer of material with a complete overlap of said previously applied layer of material with an overlapping portion of the material present in its thickness and having a thickness strictly less than the nominal height.

EFFECT: reduction in the formation of empty spaces, which leads to a decrease in the mechanical strength of the porous carrier.

18 cl, 40 dwg

Description

Field of technology to which the invention relates

This invention relates to a method for producing a monolithic inorganic porous support, which can be used, in particular, to produce a filtration membrane, and in particular a tangential filtration membrane. Specifically, the porous support is produced using additive material addition technology.

State of the art

A filtration membrane forms a selective barrier and, under the influence of transport forces, allows certain components of the fluid to pass through or be retained. The passage or retention of components can depend on their size relative to the pore size of the membrane, which then acts as a filter. Depending on the pore size, these technologies are called microfiltration, ultrafiltration, or nanofiltration.

The membrane is formed from a porous support onto which one or more separating layers are applied. Traditionally, the support is first shaped by extrusion. The support is then sintered to achieve the desired hardness while maintaining an open and interconnected porous structure. This method requires the creation of linear channels, within which the separating layer or layers are then applied and sintered. The resulting membrane undergoes at least two sintering operations. Organic binders added during the preparation of the paste prior to extrusion are completely burned off during sintering of the support.

In document FR 3006606, the applicant described the production of a filtration membrane whose porous support is manufactured using additive manufacturing through multiple deposition of a continuous powder layer, followed by localized hardening according to a predetermined pattern. This technology enables the production of mechanically robust filtration membranes used for tangential filtration. However, a disadvantage of this technology is the need to regulate the powder flowability to ensure its ideal spreading during powder deposition. Furthermore, this technology requires the removal of uncured powder for reuse, if necessary, which can be a complex, time-consuming, and expensive process, particularly when this uncured powder is located in non-linear channels of the porous support.

The applicant also proposed in documents WO 2020/109715 and WO 2020/109716 new methods for producing a porous support that overcome the drawbacks of known solutions and, in particular, are fast, easy to use, and produce a mechanically strong porous support whose shape, and in particular the shape of non-rectilinear channels, can be easily changed. The resulting porous support is uniform, mechanically strong, and has a porosity suitable for use in filtration, i.e., a porosity of 10 to 60%, which is open and interconnected, with an average pore diameter of 0.5 μm to 50 μm.

To achieve this, these methods utilize a 3D printing machine containing an extrusion head mounted movably relative to and above a fixed horizontal platform. The inorganic composition emerges from the extrusion head as a ribbon of material or a roller, enabling the construction of a manipulated, raw 3D structure based on a digital 3D model, intended to form a monolithic inorganic porous support or supports. The manipulated, raw 3D structure then undergoes a sintering step.

As described in these documents, a manipulated, raw 3D structure is achieved by superimposing layers, each corresponding to a set of continuous or discontinuous beads, either adjacent or not, extruded at the same height according to a digital 3D model. Different layers can be positioned on top of each other in different ways along the vertical axis.

Prior art from document WO 2020/109716 also discloses a method for producing a three-dimensional object by modeling with a molten filament, in which the path is created by overlapping. Patent application US 2017/165917 also describes a method for producing a three-dimensional object by modeling, in which two nozzles are used to apply material, controlled to create, in particular, an intersection between two beads of material.

Thus, the applicant proposed to produce layers by vertically depositing adjacent beads of material (c) on top of each other, as shown in Fig. 1A. The applicant noted that after the sintering operation (Fig. 1B), such a structure contained voids (v), which could have a size exceeding the size of the pores and which could reduce the mechanical strength of the porous carrier.

The applicant also proposed producing layers by depositing beads of material (c) arranged in a staggered pattern, as shown in Fig. 1C. This solution offers no benefit in terms of eliminating residual voids (v) between the beads of material. After the sintering operation (Fig. 1D), the structure still contains internal voids (v). Furthermore, this solution reduces the quality of the side surfaces, as one of the two layers has a gap, leading to settling of the material of the top layer.

Disclosure of the essence of the invention

The invention aims to eliminate the disadvantages inherent in known solutions and to propose a new method for producing an inorganic monolithic porous carrier, which avoids the formation of empty spaces that lead to a decrease in the mechanical strength of the porous carrier.

The invention is also intended to provide a method for producing a three-dimensional structure that makes it possible to control the dimensions of this three-dimensional structure and, in particular, the profile of the walls of this three-dimensional structure.

The invention is also intended to provide a method for producing a three-dimensional structure having at least one channel for circulating a processed fluid medium, containing a wall designed with the possibility of applying separating layers thereto.

The invention is also intended to provide a method for producing a three-dimensional structure comprising a wall with a continuous sequence of rounded relief elements that result in changes in the flow cross-section of the channel, while avoiding unwanted pressure losses.

In order to solve these problems, the invention proposes a method for producing at least one monolithic inorganic porous carrier containing at least one channel for circulation of the processed fluid and having a porosity of 10% to 60% and an average pore diameter in the range of 0.5 μm to 50 μm, using a 3D printing machine containing at least one extrusion head mounted movably in space above a fixed horizontal platform and moved sequentially with a nominal height along a predetermined digital trajectory for applying superimposed layers of material, each of which has a nominal width and thickness determined between the lower surface and the upper surface, wherein said 3D printing machine ensures the application of material in the form of:

- a roller with rounded edges for the purpose of creating on the wall of at least one circulation channel rounded peripheral relief elements that participate in the creation of vortices,

- compositions for constructing, on the specified horizontal platform, along a predetermined digital trajectory of the walls of a manipulated unprocessed three-dimensional structure intended for the formation of a monolithic inorganic porous carrier or monolithic inorganic porous carriers, wherein within the framework of the method:

- for a wall whose width exceeds the nominal width of the applied layer of material, the digital trajectory is divided exclusively into paths with overlapping and paths with crossing;

- feed the composition to the extrusion head of the 3D printing machine,

- the extrusion head is controlled along a digital trajectory in order to:

-- for the overlapping path, the material, during application, partially overlaps at least one edge of the previously applied layer of material with an overlapping portion of the material present in its thickness and having a thickness strictly less than the nominal height, in order to avoid, in the interior of the manipulated unprocessed three-dimensional structure, spaces between the rounded edges of the applied layer of material and the edges of the previously applied layer of material,

-- for the crossing path, the material during application crossed with at least one previously applied layer of material with a complete overlap of said previously applied layer of material by an overlapping portion of the material present in its thickness and having a thickness strictly less than the nominal height in order to avoid, in the interior of the manipulated unprocessed three-dimensional structure, spaces between the rounded edges of the applied layer of material and the edges of the previously applied layer of material.

According to a preferred embodiment feature, the extrusion head is mounted movable along a predetermined digital trajectory to perform a sequence of revolutions, each of which corresponds to a traversed path, in order to end up in the same position in a horizontal plane with an elevation corresponding to a nominal height.

According to another preferred embodiment feature, the extrusion head is controlled in such a way that, in at least one revolution, the extrusion head is raised at least once to an intermediate height, which is a fraction of the nominal height.

According to another preferred feature of the invention, the extrusion head is controlled in such a way that in at least one revolution the extrusion head is at different points along the path, rising at each point by a height increment, the sum of which corresponds to the nominal height.

Preferably, the extrusion head is controlled such that, through successive revolutions, the extrusion head is raised to build a manipulated raw three-dimensional structure in accordance with a digital 3D model, following a trajectory with continuous material deposition from the start to the completion of the construction of the manipulated raw three-dimensional structure.

According to a preferred feature, the extrusion head is controlled such that during each revolution the extrusion head is displaced in a horizontal plane so that the material being applied partially overlaps the edge of a previously applied layer of material.

For the crossing path, the extrusion head is controlled in such a way as to reduce the amount of material applied and to obtain an overlapping portion of material having a thickness strictly less than the nominal height.

For a path with equal overlap, the extrusion head is controlled to maintain a constant flow rate of applied material.

For the overlapping path, the extrusion head is controlled to adjust its position in the plane to determine the degree of overlap of the overlapping portion of the material on the previously applied layer of material.

For the overlapping path, the flow rate of the extrusion head is adjusted depending on the degree of overlap of the overlapping portion of the material on the previously applied layer of material.

Typically, the extrusion head is mounted to move along a predetermined digital path to deposit layers on top of each other in sheets, each rising to a nominal height.

According to another feature of the invention, the extrusion head is controlled in such a way as to create in the manipulated unprocessed three-dimensional structure at least one channel for circulation of the processed fluid medium, comprising a wall having a sequence of rounded relief elements that create changes in the cross-section of the channel, wherein these rounded relief elements are formed by a part of the material located opposite to the overlapping part of the material.

According to another feature, the extrusion parameters are adjusted, and the extrusion head is designed in such a way that the part of the material located opposite to the overlapping part of the material has a rounded edge.

Classically, the manipulated, raw 3D structure is placed in a heat treatment furnace to perform the sintering operation.

The invention is also intended to provide a method for producing a tangential filtration membrane, which includes the production of a monolithic inorganic porous carrier in which at least one channel for the circulation of the fluid being processed is formed, followed by the step of creating at least one separating layer on the walls of the channel or channels after sintering of said carrier.

Another object of the invention is a monolithic inorganic porous carrier manufactured using the claimed method and containing an outer surface having a sequence of rounded peripheral relief elements, and a circulation channel, the wall of which has rounded peripheral relief elements that participate in the creation of vortices.

Another object of the invention is a tangential filtration membrane containing a monolithic inorganic porous carrier equipped with at least one channel for circulation of the processed fluid, the wall of which with rounded peripheral relief elements is covered with at least one separating layer.

Brief description of the drawings

Fig. 1A shows a sectional view of a wall made by vertically layering applied beads of material, where empty spaces are shown;

Fig. 1B shows a view of the wall shown in Fig. 1A, showing the remaining empty spaces;

Fig. 1C shows a sectional view of a wall made by vertically layering staggered layers of material, showing empty spaces;

Fig. 1D is a view of the wall shown in Fig. 1C after the sintering operation, showing the remaining empty spaces;

Fig. 2A shows a schematic view of a 3D printing machine that allows the invention to be used;

Fig. 2B shows a perspective view of an example of the implementation of a manipulated raw three-dimensional structure;

Fig. 3 is a schematic top view illustrating the application of material in a conventional mode to produce a tubular wall with a width equal to the nominal width of the applied layer of material;

Fig. 3A is a sectional view taken substantially along lines A-A of Fig. 3 showing the application of successive layers of material in a conventional manner to produce a tubular wall;

Fig. 4 is a schematic top view illustrating the application of material in a vase mode to produce a tubular wall with a width equal to the nominal width of the applied layer of material;

Fig. 4A is a sectional view substantially along lines A-A of Fig. 4 showing the application of successive layers of material in a vase mode to produce a tubular wall;

Fig. 5 shows a schematic top view illustrating, within the framework of the invention, the principle of applying material to a path with overlapping of the extrusion head;

Fig. 5A is a sectional view taken substantially along lines A-A of Fig. 5 showing the overlapping of layers of material for the die overlap path;

Fig. 6 is a schematic top view illustrating the application of material to a cross-die path;

Fig. 6A is a sectional view taken substantially along lines A-A of Fig. 6 showing the application of layers of material with overlapping within the scope of the invention for a crossover die path;

Fig. 6B is a sectional view taken substantially along lines B-B of Fig. 6 showing the application of layers of material with overlapping within the framework of the invention for a cross-die path;

Fig. 7 is a schematic top view illustrating a step of the principle of applying material in a sequential vase mode to obtain a tubular wall with a width exceeding the nominal width of the material layer;

Fig. 7A is a sectional view substantially along lines A-A of Fig. 7, illustrating a step in the principle of applying material in a sequential vase mode to obtain a tubular wall of a width exceeding the nominal width of the material layer;

Fig. 7B is a schematic top view illustrating a passage for applying material in a sequential vase mode to produce a tubular wall with a width greater than the nominal width of the material layer;

Fig. 8 is a schematic top view illustrating another step in the principle of applying material in a sequential vase mode to produce a tubular wall with a width exceeding the nominal width of the material layer;

Fig. 8A is a sectional view substantially along lines A-A of Fig. 8, illustrating an arc step of the principle of applying material in a sequential vase mode to obtain a tubular wall of a width exceeding the nominal width of the material layer;

Fig. 8B is a schematic top view illustrating a passage for applying material in a sequential vase mode to produce a tubular wall with a width greater than the nominal width of the material layer;

Fig. 8C is a view illustrating another step of the principle of applying material in a sequential vase mode to produce a tubular wall with a width exceeding the nominal width of the material layer;

Fig. 9 is a schematic top view illustrating a step in the principle of applying material in a continuous mode to a vase to obtain a tubular wall with a width exceeding the nominal width of the material layer;

Fig. 9A is a sectional view substantially along lines A-A of Fig. 9, illustrating a step in the principle of applying material in a continuous mode to a vase to obtain a tubular wall of a width exceeding the nominal width of the material layer;

Fig. 9B is a schematic top view illustrating a passage for applying material in a continuous mode to a vase to produce a tubular wall with a width greater than the nominal width of the material layer;

Fig. 10 is a schematic top view illustrating another step in the principle of applying material in a continuous mode to a vase to produce a tubular wall with a width exceeding the nominal width of the material layer;

Fig. 10A is a sectional view substantially along lines A-A of Fig. 10, illustrating another step in the principle of applying material in a continuous mode to a vase to produce a tubular wall of a width exceeding the nominal width of the material layer;

Fig. 10B is a schematic top view illustrating a passage for applying material in a continuous mode to a vase to produce a tubular wall with a width greater than the nominal width of the material layer;

Fig. 10C is a schematic view illustrating another step in the principle of applying material in a continuous mode to a vase to produce a tubular wall with a width exceeding the nominal width of the material layer;

Fig. 11 shows a diagram illustrating an example of the passage of an extrusion head for a method called "sequential vase mode" and for a method called "continuous vase mode";

Fig. 12A is a top view illustrating another example of the embodiment of a wall that limits two adjacent channels and has a width twice the nominal width of the material layer;

Fig. 12B is a sectional view taken substantially along lines B-B of Fig. 12A;

Fig. 13A shows a sectional view of the application of material, carried out using a known method, for a path with an intersection before passing the intersection;

Fig. 13B shows a sectional view of the application of material, carried out using a known method, for a path with a crossing during the passage of the crossing;

Fig. 13C shows a sectional view of the application of material, carried out using a known method, for a path with a crossing after passing the crossing;

Fig. 13D shows a sectional view of the application of material, carried out using a known method, for a crossing path with overlapping of a previously applied layer of material;

Fig. 13E shows a sectional view of the application of material carried out using a known method, for a path with crossing with overlapping of a previously applied layer of material and showing the creation of empty spaces at the level of crossing of the layers of material;

Fig. 14 shows a sectional view of an example of an embodiment of the claimed invention with the application of layers of material one above the other in layers in accordance with the principle of the invention;

Fig. 15 shows a view in an inclined section of a monolithic inorganic porous carrier with eight filtration channels showing the absence of empty spaces;

Fig. 16 shows a view in direct section of a tangential filtration membrane containing a monolithic inorganic porous carrier with eight channels, the wall of which with rounded peripheral relief elements is covered with a separating layer.

Description of embodiments

The invention relates to the production of a monolithic inorganic porous carrier 1 (Fig. 2B), intended to form an element for separating a processed liquid medium by tangential flow into a filtrate (or permeate) and a retentate and commonly referred to as a tangential filtration membrane.

In many applications, such porous supports have a tubular geometry and contain at least one channel or circulation path for the fluid being processed, equipped with at least one separating layer. These circulation channels have an inlet and an outlet. Typically, the inlet of the circulation channels is located at one end of the porous support, with this end serving as the inlet zone for the fluid being processed, and the outlet is located at the other end of the porous support, serving as the outlet zone for the retentate. The inlet and outlet zones are connected by a continuous peripheral zone, where the permeate is collected.

In other application scenarios, porous carriers may comprise a block, such as a parallelepiped, containing at least one channel or circulation path for the fluid being processed, equipped with at least one separating layer. Permeate is collected at the periphery of the block or via a collector circuit within the block. In the examples presented, the porous carrier has a tubular geometry, but it is clear that the invention can be applied to porous carriers of any shape.

When the porosity (average pore diameter) of the sintered carrier is adapted to the fluid being processed (filtration threshold), said sintered carrier can be directly used in filtration and is called an auto-membrane or homogeneous membrane.

When the porosity of the sintered support is not adapted to the fluid being processed (the pore diameter is too large relative to the required filtration threshold), the walls of the circulation channel(s) are coated with at least one continuous separating layer, which ensures the filtration of the fluid being processed. The separating layer(s) are porous, and the average pore diameter in them is smaller than the average pore diameter of the support. The separating layer can be applied directly to the porous support (the case of a single-layer separating layer) or to an intermediate layer with a smaller average pore diameter applied directly to the porous support (the case of a multilayer separating layer). Thus, a portion of the fluid being processed passes through the separating layer(s) and through the porous support, and this treated portion of the fluid, called the permeate, flows down the outer peripheral surface of the porous support. The separation layers define the surface of the filtration membrane which is intended to come into contact with the fluid being processed and in contact with which the fluid being processed circulates.

The porosity of monolithic inorganic support 1 is open, meaning it forms a network of pores interconnected in three dimensions, allowing the fluid filtered by the separating layer(s) to pass through the porous support and ensure its collection at the periphery. Thus, the permeate is collected on the peripheral surface of the porous support.

The monolithic inorganic porous carrier 1 has an average pore diameter in the range of 0.5 μm to 50 μm. The porosity of the monolithic inorganic porous carrier 1 ranges from 10 to 60%, preferably from 20 to 50%.

The mean pore diameter is the d50 value of the volume distribution, where 50% of the total pore volume corresponds to pores with a diameter smaller than this d50 value. The volume distribution is a curve (analytical function) displaying the frequencies of pore volumes as a function of their diameter. The d50 value corresponds to the median, which divides the area under the frequency curve obtained by mercury porosimetry into two equal parts. Specifically, the technology described in ISO 15901-1:2005 can be used for porosimetry measurements.

The porosity of a carrier, which corresponds to the total volume of interconnected voids (pores) present in the material under consideration, is a physical quantity ranging from 0 to 1, or from 0% to 100%. It determines the transmission and retention capacities of a given porous body. For a material to be suitable for filtration, the total interconnected open porosity must be at least 10% to ensure satisfactory filtrate flow through the carrier and at most 60% to ensure adequate mechanical strength of the porous carrier.

The porosity of a porous support can be measured by determining the volume of liquid contained within the porous body and weighing the material before and after prolonged exposure to the liquid (water or another solvent). Given the known density values of the material and the liquid used, the mass difference, converted to volume, directly reflects the pore volume and, therefore, the total open porosity of the porous support.

The total open porosity of a porous body can also be accurately measured using other methods, including:

- mercury porosimetry (the above-mentioned ISO 15901-1 standard): mercury injected under pressure fills the pores accessible at the applied pressure values, and the volume of mercury injected corresponds to the volume of the pores;

- small-angle diffusion: this method, which uses either neutron or X-ray emission, provides access to average physical quantities across the entire sample. The measurement consists of analyzing the angular distribution of the intensity scattered by the sample;

- analysis of two-dimensional images obtained using a microscope;

- analysis of three-dimensional images obtained using X-ray tomography.

Furthermore, the monolithic inorganic porous carrier 1 has a mechanical strength adapted for use in tangential filtration. In particular, the monolithic inorganic porous carrier 1 withstands an internal pressure of at least 10 bar without rupture, preferably at least 30 bar without rupture, and even more preferably at least 50 bar without rupture. According to the invention, the rupture pressure corresponds to the pressure at which the carrier, the pores of which have been previously sealed (with a hot-melt material, such as paraffin), ruptures under the action of an internal excess pressure relative to the external pressure of the carrier, wherein this excess pressure is applied in channels containing water, wherein the external pressure of the carrier is atmospheric pressure.

As follows, in particular, from Fig. 2A, the claimed monolithic inorganic porous support 1 is obtained by sintering a manipulated, unprocessed three-dimensional structure 2, which is constructed in accordance with a digital 3D model M by superimposing layers 3 of the material of the composition 4 in a general sense. The layers of material are applied using a three-dimensional printing machine containing a horizontal platform 5, which can be removable and above which at least one extrusion head 6 is located.

The "raw three-dimensional structure" 2 refers to the three-dimensional structure obtained by superimposing layers of the composition 4 that have not yet been sintered. The shape and dimensions of this raw structure are determined layer by layer using a digital 3D model M, as will be explained in more detail in the following description. The digital 3D model M is determined using a computer program to construct the raw three-dimensional structure 2.

This unprocessed three-dimensional structure 2 is called "manipulable" because it does not deform under its own weight and can even tilt, thanks to accelerated hardening, which imparts durable mechanical strength, as will be explained below. Thus, this unprocessed three-dimensional structure 2 can be removed from the horizontal platform 5 and moved without deformation or breakage, particularly for the subsequent heat treatment required to obtain the porous support according to the invention.

The extrusion head 6 of the three-dimensional printing machine is mounted on a movement mechanism (not shown in the figures), such as a robot, which ensures its movement along at least three axes (x, y, and z). Thus, the extrusion head 6 can be moved in the horizontal plane (x and y axes) and vertically (z axis) using a movement mechanism controlled by a computer R of any known type. This computer R controls the movements of the movement system and, consequently, the extrusion head 6 along a trajectory predetermined depending on a digital 3D model M, on the basis of which the raw three-dimensional structure 1 is created, which allows for the production of a monolithic inorganic porous carrier 1 after the thermal processing operation.

The extrusion head 6 comprises an inlet for the composition 4 (not shown in the figures). As shown in the figures, the extrusion head 6 also comprises an extrusion nozzle having a calibrated through-hole 8, from which the composition 4 emerges. The extrusion head 6 and, consequently, the extrusion nozzle with its through-hole 8, fixedly connected to the extrusion head 6, are movable in accordance with the said digital 3D model M. According to the claimed method, the composition 4 enters the extrusion head 6 of the machine through the inlet to feed the through-hole 8. A mechanical action can be used to feed the composition 4 into the head 6 through this inlet.

For the purposes of this invention, "mechanical action" refers to the application of pressure using any known technical means, such as a piston, pump, or screw. This step can be performed in a conventional manner known to those skilled in the art and is not described here. The material exits the orifice 8 due to a predetermined pressure exceeding atmospheric pressure. This creates a force that acts vertically downward on the material during extrusion and compresses the material between the extrusion nozzle and the underlying solidified material.

The through-hole 8 is located opposite and near the horizontal platform 5. The through-hole 8 is movable in the vertical direction (i.e., along the z-axis) and in the horizontal direction (i.e., along the x- and y-axes) relative to the horizontal platform 5, which is fixed. The vertical and/or horizontal movement of the through-hole 8 relative to the fixed horizontal platform ensures the construction, in accordance with the digital 3D model M, of a manipulated, unprocessed three-dimensional structure 2 in a position of support on the horizontal platform 5 as a result of the extrusion of a bead of material through the through-hole 8.

According to the embodiment shown in the figures, the extrusion head 6 is equipped with a circular cross-section orifice 8. When the orifice 8 has a circular cross-section, its diameter is preferably from 0.1 mm to 10 mm, preferably from 0.1 mm to 1 mm, and even more preferably from 0.2 mm to 0.8 mm.

It may be recalled that a predetermined extrusion flow rate E (e.g. determined by the rotation speed of the extrusion screw), a predetermined movement speed F of the extrusion head 6 and a nominal height e of movement of the extrusion head 6 correspond to an applied layer of material 3 with a nominal width L such that L=f(E, F, e). The layer of material 3 has a straight cross-section with a nominal height e defined between a substantially flat upper surface 3s and a substantially flat lower surface 3i, connected to each other on both sides by two edges 3b of a rounded shape (Figs. 3 and 3A). The nominal width L of the layer of material 3 can thus be adjusted or changed depending on the movement speed F and/or on the extrusion flow rate of the extrusion head 6.

A composition 4 is fed to the extrusion head 6, for example in the form of a paste, as described, for example, in document PCT/FR2019/052807, or in the form of a thread or granules, as described in document PCT/FR2019/052808. Preferably, the composition 4 is an inorganic composition, typically of a ceramic and/or metallic nature.

The ceramic composition consists of a powdered solid inorganic phase and a matrix.

The powdered solid inorganic phase of the ceramic composition includes one or more solid inorganic materials, each in the form of particles with an average diameter ranging from 0.1 μm to 150 μm.

The concept of mean diameter is related to the concept of particle distribution. Indeed, powder particles rarely have a uniform or monodisperse size, and therefore, a powder is most often characterized by its particle size distribution. The mean diameter corresponds to the mean value of the particle size distribution. Distribution can be represented in various ways, for example, as a frequency or cumulative distribution. Some measurement methods directly yield a distribution based on count (microscopy) or mass (sieving). The mean size is a measure of central tendency.

Among the most commonly used central tendencies are the mode, median, and mean. The mode is the most frequent diameter in a distribution: it corresponds to the maximum of the frequency curve. The median represents the value at which the overall frequency of values is the same both above and below the median (in other words, the number or total volume of particles is the same both below and above the median). The mean is calculated and defines the point at which the moments of the distribution are equal. In a normal distribution, the mode, mean, and median coincide, while they differ in a non-normal distribution.

The average diameter of the particles included in the inorganic powder is measured, in particular, by:

- laser light diffraction for particles from 3 mm to approximately 0.1 µm:

- sedimentation/centrifugation;

- dynamic light scattering (DLS) for particles from 0.5 µm to 2 nm;

- analysis of images obtained using a microscope;

- small-angle X-ray diffraction.

The granularity of a solid inorganic powder phase refers to the size of the particles that make up the solid inorganic powder phase. Granularity is characterized by the concept of average diameter described above.

Most often, the ceramic composition comprises, as the powdered ceramic material(s), alone or in a mixture, an oxide and/or nitride and/or a carbide. In particular, examples of oxides that can be used in the context of the invention include metallic oxides, in particular titanium oxide, zirconium oxide, aluminum oxide, and magnesium oxide, with titanium oxide being the most preferred. Examples of carbides that can be mentioned include, in particular, metallic carbides, in particular silicon carbide. Examples of nitrides that can be used include, in particular, titanium nitride, aluminum nitride, and boron nitride. According to a preferred embodiment, the ceramic composition comprises at least one metal oxide as the inorganic powdered material, and preferably titanium oxide.

Within the framework of the invention, the ceramic composition has rheological properties adapted in terms of plasticity for its extrusion through the extrusion head 6.

According to the first embodiment, the matrix of the ceramic composition contains one or more solvents. The solvent or solvents may be aqueous or organic. For example, water, ethanol, or acetone may be used.

Furthermore, the matrix of the ceramic composition contains one or more organic additives. Preferably, these organic additives are soluble in the matrix solvent or solvents. Within the scope of the invention, the organic additive or additives may be selected from, but are not limited to, the following:

- binders, for example, among cellulose ethers such as hydroxyethyl cellulose, which is a polymer, gum arabic, which is a polysaccharide, or polyethylene glycol (PEG);

- lubricants and plasticizers, such as glycerin or stearic acid;

- thickeners and gelling agents, such as xanthan gum or agar-agar, which is a polymer of galactose.

The mass content of powdered inorganic material(s) in the ceramic composition may be from 50 to 90%, preferably from 80 to 85 wt.% relative to the total mass of the ceramic composition.

The mass content of the matrix in the ceramic composition may be from 10 wt.% to 50 wt.%, preferably from 15 to 20 wt.% relative to the total mass of the ceramic composition.

This ceramic composition is not a powder, but a paste. The rheology of this ceramic composition can be controlled by the granularity of the powdered solid inorganic phase and/or by the nature of the organic additives, if present, and/or by their respective proportions. Indeed, for example, using a matrix containing one or more organic additives soluble in one or more solvents incorporated into the matrix allows for the rheology of the ceramic composition to be modified.

According to a second embodiment, the ceramic composition comprises a matrix consisting of one or more thermoplastic polymers. The matrix is organic in nature and is solid at ambient temperature.

By "hot-melt polymer" we mean a polymer that softens when exposed to heat.

As examples of a hot-melt polymer that can be used within the framework of the invention, the following polymers or a family of polymers, possibly functionalized, used alone or in a mixture in a matrix, can be mentioned: polylactic acid (PLA), polyvinyl alcohol (PVA), acrylonitrile-butadiene-styrene (ABS), polypropylene (PP), polyethylene, polyethylene terephthalate (PET), thermoplastic polyurethane (TPU), polyolefins, thermoplastic elastomers (TPE), elastomers based on polyolefin (TPE-O) and polycarbonate.

The mass content of powdered inorganic material(s) in the ceramic composition may be from 40 to 95%, preferably from 70 to 90 wt.% relative to the total mass of the ceramic composition.

In the context of the invention, the ceramic composition, preferably in granular form, is preheated upstream so that the hot-melt polymer or polymers soften and the ceramic composition can be subjected to pressure at the inlet of the outlet orifice 8. Typically, the extrusion head 6 is heated to soften the hot-melt polymer or polymers, which enables the extrusion of the ceramic composition. The temperature of the extrusion head 6 and the outlet orifice 8 can be adjusted depending on the hot-melt polymer or polymers present in the ceramic composition.

Furthermore, within the framework of the invention, it is possible to regulate the rheology of the ceramic composition by means of its temperature in the extrusion head, and/or due to the granularity of the powdered solid inorganic phase, and/or due to the nature of the hot-melt polymer or hot-melt polymers, and/or due to their proportions.

According to the invention, the claimed method divides the digital trajectory into paths to avoid creating spaces between the rounded edges of the applied material layer and the edges of the previously applied material layer within the interior of the manipulated, unprocessed three-dimensional structure. As shown in Figs. 1A and 1C, applying material beads contiguously in prior art solutions results in the creation of material voids that remain after sintering and can reduce the mechanical strength of the monolithic inorganic porous support.

The claimed method determines whether the manipulated, unprocessed three-dimensional structure contains a wall whose width is equal to or greater than the nominal width L of the material layer. Indeed, for a wall whose width is equal to the nominal width L of the material layer, this wall is constructed using layers of material that are exclusively placed one above the other without creating voids. For this type of wall, it can be noted that applying beads of material one above the other does not create voids except when the trajectory contains a crossover, as shown in Figs. 6 and 13A-13E.

As shown in Fig. 6, a crossover path occurs for a figure-eight structure. Crossover occurs when a self-closing trajectory returns to point I with coordinates Xi, Yi, where a layer of material (of order n-1) has already been deposited. Passage through the layer of material (of order n-1) occurs when the currently deposited layer of material (of order n) comes into contact with the previously deposited layer of material (Fig. 13A). In this case, the extrusion of the material is stopped (Fig. 13B), sliding is performed at the same height, and extrusion is resumed after the exit edge of layer of order n-1 (Fig. 13C). A layer of material of order n+1 is superimposed on a layer of material of order n-1, and the passage of this new layer of material is performed as described above (Figs. 13D and 13E). As clearly shown in the figures, placing two layers of material next to each other or adjacent to each other while completely passing through a previously applied layer of material results in the creation of voids.

Fig. 3 and 3A illustrate a first embodiment, called the conventional mode, for producing a wall 10 whose width is equal to the nominal width L of the material layer. For example, this wall 10 is part of a manipulated unprocessed three-dimensional structure in the form of a carrier of a circular cross-section, having a single central channel 11. The trajectory of the extrusion head 6 is divided into circular paths with an average diameter D, each of length nD and with an elevation of the extrusion head 6 along the vertical axis with increments e at each revolution. The extrusion head 6 makes the first revolution t, being positioned at an elevation e relative to the level of the platform 5, and extrudes a constant amount of material to deposit a layer of material of constant thickness e. For example, arrow F in this case indicates the counterclockwise direction of movement of the extrusion head 6. Upon completion of the first revolution t, the extrusion head 6 rises to a height equal to the thickness e of the material layer to make a second revolution, extruding a constant amount of material to continuously deposit the material. Layers of material 3 are thus deposited until the required height is reached.

Fig. 4 and 4A illustrate a second embodiment, called a vase mode, for producing a wall 10, for example in the case of a manipulated raw three-dimensional structure in the form of a carrier of circular cross-section having a single central channel 11. The trajectory of the extrusion head 6 is divided into circular paths with an average diameter D, each of length nD and with an elevation of the extrusion head 6 along the vertical axis with successive increments in such a way that at the end of each revolution the sum of these increments makes it possible to obtain a layer of material of thickness e at each revolution.

During the first revolution t, the extrusion head extrudes an increasing amount of material proportional to its position on the inclined plane with an average slope e/nD. Upon completion of the first revolution t, the extrusion head 6 makes a second revolution, following the same average slope e/nD and extruding a constant amount of material for a continuous deposition of material with an elevation corresponding to the thickness e. Layers of material 3 are thus deposited until the required height is achieved.

In the case where the manipulated, unprocessed three-dimensional structure comprises a wall whose width exceeds the nominal width L of the material layer, the material layers must be constructed in accordance with the invention, since it becomes impossible to construct this wall solely by means of superimposed material layers. According to the invention, the method provides for interleaving of the layers of material 3 as a result of alternating overlapping and/or crossing of said layers of material 3, in order to avoid the creation of spaces or voids between the layers of material. Within the framework of the invention, interleaving is understood, regardless of the definition provided by quantum mechanics, as a state of material layers interleaved due to overlapping and/or crossing.

Thus, for wall 10, the width of which exceeds the nominal width L of material layer 3, within the framework of the claimed method, the digital trajectory of extrusion head 6 is broken down exclusively into overlapping and/or crossing paths. Clearly, extrusion head 6 (or, more precisely, its supporting carriage) follows a trajectory point by point, completely defined from the beginning to the end of the manufacturing process of the manipulated, raw three-dimensional structure 2 by a sequence of points. Each of these points is predetermined in space by its Cartesian coordinates Xi, Yi, Zi. The coordinates Xi and Yi precisely determine the position of the center of the circular opening 8 of the extrusion nozzle. Thus, extrusion head 6 moves from point A (Xa, Ya, Za) to point B (Xb, Yb, Zb), following vector AB, then from point B to point C, following vector AC, and so on, in accordance with a sequence of command series called G-code commands of the intermediate program between the digital 3D model and the printing machine. It should be noted that, in addition to determining the trajectory at each of its points, defined by Cartesian coordinates Xi, Yi, Zi, all parameters are determined for each of these points, in particular, the extrusion flow rate E and the movement speed F of extrusion head 6.

It is clear that the digital trajectory of the extrusion head 6 is divided into overlapping paths and crossing paths. As shown in Figs. 5 and 5a, the overlapping path corresponds to the part of the trajectory, in which the layer of material 3 (of the order n) partially overlaps at least one edge 3b of the previously applied material 3 (of the order n-1), in order to avoid spaces between the rounded edges of the applied material and the edges of the previously applied material in the inner part of the manipulated unprocessed three-dimensional structure. As shown, in particular, in Fig. 5A, the applied material (of the order n) partially overlaps at least one edge 3b of the previously applied material 3 (of the order n-1) with the overlapping part of the material present in its thickness, that is, between the upper side 3s and the lower side 3i of said applied layer. In addition, this overlapping part of the material 3c has a thickness strictly less than the nominal height e.

According to the feature of the claimed method, for the overlapping path, the extrusion head 6 is controlled in such a way as to regulate the extrusion flow rate depending on the degree of overlap of the overlapping portion of the material on the previously applied layer of material.

The crossing path corresponds, as shown in Fig. 6A and 6B, to a portion of the trajectory in which the current applied material layer (of order n) crosses at least one previously applied material layer (of order n-1) with a complete overlap of said previously applied material layer, in order to avoid spaces between the rounded edges of the applied material and the edges of the previously applied material in the interior of the manipulated unprocessed three-dimensional structure. In the crossing path, the material during application (of order n) completely overlaps the previously applied material layer (of order n-1) with the overlapping portion of material 3c, i.e., passing from at least one edge 3b to the other of the previously applied material layer. This crossing between these two material layers can occur in any possible angular positions between the directions of these two material layers. The overlapping portion of material 3c is considered in the thickness of the current applied material layer, i.e., between the upper side and the lower side of said applied layer. In addition, this overlapping part of material 3c has a thickness strictly less than the nominal height e.

From the above description, one can deduce the alternation between the layers of material 3. Such alternation exists from the moment when, during a rotation, there is at least one overlapping path and/or one crossing path. Each subsequent rotation, which necessarily "covers" the previous overlap(s) and/or the previous crossing(s), performs alternation of the layers of material 3. Thus, the alternation of the layers of material is the result of multiple rotations, each of which has at least one overlapping path and/or one crossing path.

According to the feature of the claimed method, for the crossing path, the extrusion head 6 is controlled in such a way as to reduce the amount of material applied and to obtain an overlapping portion of material having a thickness strictly less than the nominal height e. Thus, as clearly shown in Fig. 6A and 6B, each layer of material has a nominal height e, except in the case opposite or during passage over an already obtained layer of material.

Thus, as shown in Fig. 6A and 6B, the first layer of material n is made with a thickness less than the nominal height e, for example, equal to e/2. For a layer of material n that intersects with a previously made layer of material n-1, this layer of material n is obtained with a nominal thickness e, except for the case when it overlaps the previous layer of material n-1. When the extrusion head is located directly above the layer of material, the extrusion flow rate is reduced such that the overlapping portion 3b of the layer has a thickness less than the nominal thickness e, equal to e/2 in the example shown. Thus, the crossing paths obtained in accordance with the principle of the invention do not have voids, in contrast to the known solution shown in Fig. 13C-13E.

According to a preferred embodiment of the invention, the extrusion head 6 is movably mounted along a predetermined digital trajectory T to perform a sequence of revolutions t, each of which corresponds to a traversed path in order to end up in the same position in the horizontal plane with an elevation corresponding to a nominal height e. In other words, the digital trajectory of the extrusion head 6 is divided into revolutions, considering that for each revolution the extrusion head 6 rises to a nominal height e. Naturally, the number of revolutions t is selected in such a way as to obtain the required height for the manipulated unprocessed three-dimensional structure 2.

At each of these revolutions, the extrusion head 6 passes through one or more overlapping paths and/or one or more crossing paths. For each of these revolutions, the extrusion head 6 performs a pass formed by a sequence of points with coordinates Xi, Yi, Zi, as indicated above, with the possibility of elevation along the vertical axis at one or more of these points.

According to a first embodiment, described in particular with reference to Figs. 7-7B and 8-8C, the method provides for controlling the extrusion head 6 in such a way that at least in one revolution the extrusion head is raised at least once to an intermediate height, which is a fraction of the nominal height e.

According to a second embodiment, described in particular with reference to Figs. 9-9B and 10-10C, the method provides for controlling the extrusion head 6 in such a way that at least on one revolution the extrusion head is located at different points along the path, rising at each point by a height increment, the sum of which corresponds to the nominal height e.

The description presented with reference to Figs. 7-7B and 8-8C concerns a first example of the implementation of the method called the "sequential vase mode," according to which a portion of the path is built at the same height a (e.g., a=e/2), then the elevation is incremented by the value a to complete a revolution and cover the previous layer with an overlapping portion with the value a. According to this method, the nominal height e is an integer multiple of a.

In Fig. 7B the first half of the path passed by the extrusion head 6 is shown, corresponding to a circle of diameter D1. As shown in Fig. 7 and 7A, the first bead of material 3 is applied to the horizontal platform 5 with a rise equal to e/2, continuing throughout the entire passage of the circle of diameter D1. Within the framework of the invention, this passage, which covers the circle by 360°, corresponds to half a revolution. After passing this half a revolution at one height e/2, the extrusion head 6 and, consequently, the center of the throughput opening 8 are shifted radially towards the center of the circle by a distance equal to d = (D2 - D1)/2 and rise by an increment equal to e/2, following the circle of diameter D2 (Fig. 8A, 8B). As a result, a layer of material is obtained, which partially overlaps the inner edge 3b of the previously applied layer of material with an overlapping portion 3c of the material, present in its thickness. It should be noted that the overlapping part 3c of the material has a thickness strictly less than the nominal height e. Thus, the extrusion head 6 has passed a revolution t within the framework of the invention, corresponding to a path along a circle of diameter D1, and then along a circle of diameter D2 (Fig. 8B).

In the position shown in Fig. 8A, the extrusion head 6 (and, consequently, the center of the throughput opening 8) is displaced radially outward from the circumference D2 by a distance equal to d and is again raised by an increment of e/2, partially overlapping the previous layer of material along the circumference D1. As a result, a layer of material is obtained that partially overlaps the outer edge 3b of the previously applied layer of material with an overlapping portion 3d present in its thickness. The overlapping portion 3d of the material has a thickness strictly less than the nominal height e. The extrusion head 6 is displaced radially inward from the circumference D1 by a distance equal to d and is again raised by an increment of e/2, partially overlapping the previous layer of material along the circumference D2. As a result, a layer of material is obtained that partially overlaps the inner edge 3b of the previously applied layer of material with an overlapping portion 3c present in its thickness. Thus, the extrusion head 6 has passed the second revolution t within the framework of the invention, corresponding to the path along a circle with a diameter D1, and then along a circle with a diameter D2 (Fig. 8C).

Extrusion head 6 is then controlled depending on the number of revolutions, ensuring the required height for the manipulated raw three-dimensional structure 2. It should be noted that in the example shown, the passes for the first and second revolutions are identical. Of course, it is possible to provide for the passes for different revolutions to differ. Similarly, the nominal height e for each revolution, which is identical in the example shown, may differ for different revolutions.

The description given with reference to Figs. 9-9B and 10-10C concerns a second example of the method, called the "continuous vase mode", in which the extrusion head 6 extrudes an increasing amount of material proportional to its position.

In Fig. 9B the first half of the path passed by the extrusion head 6 is shown, corresponding to a circle of diameter D1. As shown in Fig. 9 and 9A, the first bead of material 3 is applied to the horizontal platform 5 with a gradual rise, continuing throughout the entire passage of the circle of diameter D1, in order to reach a height equal to e/2 at the end of the passage of the circle D1. Within the framework of the invention, this passage corresponds to half a revolution, while it should be noted that at a quarter of a revolution the thickness of the material layer is equal to e/4. After passing this half revolution, in order to reach a height e/2, the extrusion head 6 is displaced radially towards the center of the circle by a distance equal to d = (D2 - D1) / 2 and gradually and continuously rises along the circle of diameter D1 in order to reach a height e at the end of the path passed along this diameter D1 (Fig. 10, 10A, 10B). The resulting layer of material partially overlaps the inner edge 3b of the previously applied layer of material with an overlapping portion 3d of the material present within its thickness. It should be noted that the overlapping portion of the material has a thickness strictly less than the nominal height e. Thus, extrusion head 6 has completed a revolution t within the scope of the invention, corresponding to a path along a circumference of diameter D1, and then along a circumference of diameter D2.

In the position shown in Fig. 10A, the extrusion head 6 is displaced radially outward from the circumference D2 by a distance equal to d and is gradually raised by an increment of e/2, partially overlapping the previous layer of material along the circumference D1. As a result, a layer of material is obtained that partially overlaps the outer edge 3b of the previously applied layer of material with an overlapping portion 3d present in its thickness. The overlapping portion of the material has a thickness strictly less than the nominal height e. The extrusion head 6 is displaced radially inward from the circumference D1 by a distance equal to d and is again gradually raised by an increment of e/2, partially overlapping the previous layer of material along the circumference D2. As a result, a layer of material is obtained that partially overlaps the inner edge of the previously applied layer of material with an overlapping portion present in its thickness. Thus, the extrusion head 6 has passed the second revolution t within the framework of the invention, corresponding to the path along a circle with a diameter D1, and then along a circle with a diameter D2 (Fig. 10C).

Extrusion head 6 is then controlled depending on the number of revolutions, ensuring the desired height of the manipulated raw three-dimensional structure is constructed. It should be noted that in the example shown, the passes for the first and second revolutions are identical. Of course, it is possible to design the passes for different revolutions to differ. Likewise, the nominal height for each revolution, which is identical in the example shown, may vary for different revolutions.

In Fig. 11, as an example, the curve A shows the passage of the extrusion head 6 for the method called the "sequential vase mode" and described with reference to Figs. 7-7B and 8-8C. The path is made, for example, from point to point in two stages of increments e/2. According to this example, the extrusion head 6 is controlled in such a way that at least in one revolution t the extrusion head rises at least once to an intermediate height, which is a fraction of the nominal height.

Curve B describes the passage of the extrusion head 6 for the method called the "continuous vase mode" and shown in Figs. 9-9B and 10-10C. In the example shown, each path (revolution t) is completed through fifteen points (with coordinates X, Y), that is, with fifteen increments or steps of height dZ, proportional to the distance that separates two successive points, that is, fifteen increments of the same height dZ=e/15. Thus, within the framework of the method, the extrusion head 6 is controlled so that at least in one revolution the extrusion head is at different points of the path, rising at each point by an increment of height, the sum of which corresponds to the nominal height e. It should be noted that Fig. 11 shows a curve of continuous gradual rise C, corresponding to a gradual rise along the Z axis of the extrusion head.

From the above description it follows that the extrusion head 6 is controlled so that by means of a sequence of revolutions the extrusion head is raised to construct the manipulated raw three-dimensional structure 2 in accordance with the digital 3D model, following a trajectory with continuous application of a layer of material 3 from the beginning to the end of the construction of the manipulated raw three-dimensional structure 2.

Furthermore, the extrusion head 6 is controlled such that during each revolution t, the extrusion head is displaced in the horizontal X, Y plane and such that the applied flowing material partially overlaps the edge of the previously applied layer of material. Preferably, for the overlapping path, the extrusion head 6 is controlled to regulate its position in the horizontal X, Y plane and to determine the degree of overlap of the overlapping portion of material 3d on the previously applied layer of material. As noted above, the displacement d in the horizontal X, Y plane between successive passes allows the degree of overlap between the layers of material to be selected.

In the embodiment examples illustrating the principle of the invention, it can be noted that the resulting wall has a width that can be constructed using two partially overlapping layers of material. Of course, the principle of the invention can be applied to construct a wall whose width requires a greater number of applied layers of material, as shown by way of example in Fig. 12A and 12B with three layers. According to this embodiment example, the resulting wall limits two adjacent channels and has a width with overlapping three layers. This wall is constructed in the vase mode, following the path a1+b1+c1+d1+e1+f1+g1, then along the path a2+b2+c2+d2+e2+f2+g2, then a3+b3... The flow rate of the extrusion head 6 is reduced to zero when the extrusion head 6, completing fi, reaches ei and the fork (following gi) in order to reach ai+1. The thickness values of the material layers of the first turn correspond to and are proportional to the traveled distance, while the thickness values of the layers, starting from the second turn, are equal to the nominal thickness.

According to a feature of the embodiment of the invention, for the overlapping path, the extrusion head 6 is controlled in such a way as to maintain a constant flow rate of the layer of applied material, while the flow rate of the extrusion head 6 is reduced for the crossing path.

Thus, the claimed method enables the construction of a manipulable, unprocessed three-dimensional structure 2 without the formation of voids, regardless of the shape or size of the walls. Fig. 15 illustrates an example of a manipulable, unprocessed three-dimensional structure 2 that, after sintering, has no voids in the resulting walls. The examples described above illustrate the first preferred embodiment, referred to as the conventional mode or vase mode, in which the extrusion head follows a trajectory with the continuous deposition of a layer of material 3 from the beginning to the end of the construction of the manipulable, unprocessed three-dimensional structure 2.

Fig. 14 illustrates a second embodiment in which the extrusion head 6 is movably mounted along a predetermined digital path T to apply layers of material one above the other in layers, each of which rises to a nominal height e. The application of material in layers is described, in particular, in documents WO 2020/109715 and WO 2020/109716. This method consists of forming a first layer 3 ₁ and 3 ₂ in accordance with a digital 3D model defined by a computer design program, thanks to the horizontal movement of the through hole 8 above the horizontal platform 5.

The extrusion head 6 moves horizontally and, therefore, parallel to the horizontal platform 5 along a path predetermined depending on the digital 3D model M in order to form the first layer. After applying the first layer, the extrusion head 6 moves in such a way that the applied bead forms the second layer 3 ₃ in accordance with the digital 3D model M. For this purpose, the extrusion head 6 moves vertically (i.e., along the Z axis) and horizontally (i.e., along the X and/or Y axes) to the required position. The extrusion of the inorganic composition 4 through the extrusion head 6 can be continuous or discontinuous. Thus, the second layer is applied to the first layer with the material overlapping the previously applied layer in accordance with the digital 3D model M.

Naturally, the application of the material layer is carried out to ensure overlap (complete or partial), as described above, to avoid the formation of voids between the material layers. Thus, in the example shown in Fig. 14, the layer of material 3 ₃ of the second layer partially overlaps, starting from its two opposite edges, the adjacent edges of the two previously applied layers of material 3 ₁ and 3 ₂ , which avoids the formation of voids.

The claimed method makes it possible to construct manipulated unprocessed three-dimensional structures 2 intended for forming monolithic inorganic porous carriers 1 having mechanical strength characteristics adapted for their use in tangential filtration. Preferably, the extrusion head 6 is controlled in such a way as to obtain in the manipulated unprocessed three-dimensional structure 2 at least one channel 11 for circulation of the processed fluid. The wall of this channel 11 is formed by rounded edges 3b of the material layers, located opposite to the overlapping part of the material. As shown in the drawings, the extrusion head 6 is made in such a way that the material layers have rounded edges 3b. Thus, the channel 11 comprises a wall having rounded relief elements, each of which extends along the entire periphery of the channel, being formed by the rounded edge 3b of the material layers. These peripheral rounded relief elements are located one above the other along the length of the channel, as shown in Fig. 15 and 16. On the scale of the thickness e of the material layers, these peripheral relief elements participate at their level in this channel during tangential filtration in the creation of vortices along the entire channel. In Fig. 16, it can be noted that these peripheral rounded relief elements are present even when the inner wall of the channels 11 is covered with separating layers, the profile of which appears in the form of a line in Fig. 16. Thus, the separating layer or separating layers repeat the shape of the peripheral rounded relief elements, the rounded profile of which is preserved in order to participate in the creation of vortices in the channel 11. It should be noted that the monolithic inorganic porous carrier 1, manufactured by the claimed method, has an outer surface, which also contains a sequence of peripheral rounded relief elements St, which are located one above the other along the carrier, as shown in Fig. 2B, 15 and 16.

Claims (18)

1. A method for producing at least one monolithic inorganic porous carrier (1) comprising at least one channel for circulating a processed fluid medium and having a porosity of 10% to 60% and an average pore diameter in the range of 0.5 μm to 50 μm, using a 3D printing machine (I) comprising at least one extrusion head (6) mounted with the possibility of movement in space above a fixed horizontal platform (5) and moved sequentially with a nominal height (e) along a predetermined digital trajectory (T) to apply superimposed layers of material, each of which has a nominal width and thickness determined between the lower surface and the upper surface, wherein said 3D printing machine ensures the application of material in the form of: - a roller with rounded edges to obtain on the wall of at least one circulation channel rounded peripheral relief elements that participate in the creation of vortices, - compositions (4) for constructing, on the specified horizontal platform (5), along a predetermined digital trajectory (T) the walls of a manipulated unprocessed three-dimensional structure (2) intended for the formation of a monolithic inorganic porous carrier or monolithic inorganic porous carriers (1), wherein within the framework of the method: - for a wall whose width exceeds the nominal width (L) of the applied layer of material, the digital trajectory is divided exclusively into overlapping paths and crossing paths; - feed the composition (4) to the extrusion head (6) of the 3D printing machine (I), - control the extrusion head along a digital trajectory in order to: -- for the overlapping path, the layer of material during application partially overlaps at least one edge of the previously applied layer of material with an overlapping portion of the material present in its thickness and having a thickness strictly less than the nominal height (e), in order to avoid, in the interior of the manipulated unprocessed three-dimensional structure, spaces between the rounded edges of the layer of material being applied and the edges of the previously applied layer of material, -- for a crossing path, the layer of material during application crossed at least one previously applied layer of material with a complete overlap of said previously applied layer of material by an overlapping portion of material present in its thickness and having a thickness strictly less than the nominal height (e), in order to avoid, in the interior of the manipulated unprocessed three-dimensional structure, spaces between the rounded edges of the applied layer of material and the edges of the previously applied layer of material. 2. The method according to claim 1, in which the extrusion head (6) is mounted with the possibility of movement along a predetermined digital trajectory (T) in order to carry out a sequence of revolutions, each of which corresponds to the path traveled, in order to end up in the same position in the horizontal plane with an elevation corresponding to the nominal height (e _N ). 3. The method according to claim 2, in which the extrusion head is controlled so that during at least one revolution the extrusion head is raised at least once to an intermediate height that is a fraction of the nominal height. 4. The method according to claim 2, in which the extrusion head is controlled so that in at least one revolution the extrusion head is at different points along the path, rising at each point by a height increment, the sum of which corresponds to the nominal height. 5. The method according to one of claims 2-4, in which the extrusion head is controlled so that by means of successive revolutions the extrusion head is raised to build a manipulated raw three-dimensional structure (2) in accordance with a digital 3D model (M), following a trajectory with continuous deposition of a layer of material (3) from the start to the completion of the construction of the manipulated raw three-dimensional structure (2). 6. The method according to one of paragraphs 2-5, in which the extrusion head is controlled so that during each revolution the extrusion head is displaced in the horizontal plane so that the applied material partially overlaps the edge of the previously applied layer of material. 7. The method according to one of claims 1 to 6, wherein for the crossing path the extrusion head is controlled so as to reduce the amount of material applied in order to obtain an overlapping portion of material with a thickness strictly less than the nominal height (e _N ). 8. The method according to one of paragraphs 1-7, in which for a path with equal overlap, the extrusion head is controlled so as to maintain a constant flow rate of applied material. 9. The method according to one of claims 1-8, wherein for the overlapping path the extrusion head is controlled to adjust its position in the plane to determine the degree of overlap of the overlapping portion of the material on the previously applied layer of material. 10. The method according to one of paragraphs 1-9, in which, for the overlapping path, the flow rate of the extrusion head is adjusted depending on the degree of overlap of the overlapping portion of the material on the previously applied layer of material. 11. The method according to claim 1, in which the extrusion head (6) is mounted with the possibility of movement along a predetermined digital trajectory (T) in order to superimpose layers of material on top of each other in layers, each of which rises to a nominal height (e). 12. The method according to one of claims 1-11, in which the extrusion head is controlled so as to form in the manipulated unprocessed three-dimensional structure (2) at least one channel for circulation of the processed fluid, comprising a wall having a sequence of rounded relief elements creating changes in the cross-section of the channel, wherein these rounded relief elements are formed by a part of the material located opposite to the overlapping part of the material. 13. The method according to one of claims 1-12, in which the extrusion head is designed so that the portion of the material located opposite to the overlapping portion of the material has a rounded edge. 14. The method according to one of claims 1-13, in which the manipulated unprocessed three-dimensional structure (2) is placed in a heat treatment furnace for the purpose of performing a sintering operation. 15. A method for producing a tangential filtration membrane, which includes the production, according to any of paragraphs 1-14, of a monolithic inorganic porous carrier (1), in which at least one channel (11) for the circulation of the fluid being processed is formed, followed, after sintering of said carrier, by the step of creating at least one separating layer on the walls of the channel or channels (11). 16. A monolithic inorganic porous carrier (1), manufactured according to any one of claims 1-14, having a porosity from 10% to 60% and an average pore diameter in the range from 0.5 μm to 50 μm, wherein said monolithic inorganic porous carrier contains an outer surface having a sequence of rounded peripheral relief elements (st), and at least one channel for circulation of the processed fluid medium, the wall of which has rounded peripheral relief elements that participate in the creation of vortices. 17. A tangential filtration membrane containing a monolithic inorganic porous carrier (1) according to claim 16, equipped with at least one channel (11) for circulation of the processed fluid, the wall of which with rounded peripheral relief elements is covered with at least one separating layer. 18. The tangential filtration membrane of claim 17, wherein the vortex formation created by the rounded peripheral relief elements within said channel is maintained after the application of one or more separating layer(s).